Dielectric composition



Dec. 27, 1949 F. M. CLARK 2,492,210

DIELECTRIC COMPOSITION Filed Oct. 19, 1944 Fig. l 1 79 .2.

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HIGH FREQUENCY CAPAC/TOR co/vmms LIQUID 5575/? 20 /7 OFBENZO/C AC/D -/0 0 I0 20 50 40 5'0 .90 I00 PERCENT/1658 His Attorney.

Patented Dec. 27, 1949 UNITED STATES PATENT OFFICE DIELECTRIC COMPOSITION Frank M. Clark, Pittsfield, Mass, assignor to General Electric Company, a corporation of New York Application October 19, 1944, Serial No. 559,410

4 Claims. (Cl. 252-64) 1 2 The present. application is a continuation-inheat. The insulation resistance of the benzoates part of my prior application Serial No. 493,357, had been. found to be so low as to class the benfiled July 8, 1943, and relatesto electrical capaczoates as semi-conductors, rather than promisitors which. are particularly adapted for efhcient ing dielectric materials which should have a very operation in the high frequency field. 5 high resistivity. Mineral oil, which is widely used One of the objects of my invention is to pro as a dielectric material, has a resistivity of vide capacitors adapted for operation in power ohms per centimeter. Oil, however, has a. low oscillator circuits for industrial heating or other dielectric constant (2 to 2.25) which consequently uses at frequencies of tenkilocycles up to 100% iv a c pa itor havin l w mi r r pa y kilocycles, or higher, High frequencies o t 10 per unit of volume. This is undesirable in most commonly in commercial use are in the range of high frequency capacitor applications. It is about 500 to 1000 kilocycles, surprising, therefore, to find that liquid benzoate Another object of my invention is to provide esters having much lower resistivity thanmineral capacitors adapted for operation at high ire oil operate w high efiiolenoy and ave l quencies at temperatures ranging from ordinary 15 energy losses when functioning as dielectric eleenvironmental temperatures up to about 100 (3., ments in high frequency capacitors. or even higher temperatures, with little or no My invention will be described in greater dechange in capacity. Substantial constancy of tail in connection with the accomp y g drowcapacity in high frequency circuits over the range ing. Figs. 1 and 2 of the drawing are graphs ofcommonly encountered operating temperaindicating the dielectric constant of benzoate tures isparticularly desirable in radio transmitst pe iv y, for a range f q es and ter apparatus. a range of temperatures; Figs. 3 and 4 are graphs Mica has been commonly used as capacito showing the power factor of benzoate esters over dielectric material in the h-ighf-requency field. a n e f temperatures n i h f q i Mica is characterized by a desirable low power Fig. 5 is a graph ShoWing h f ow points OfmlX- fa tor, namely ab t 0.1 e t, H t tures of benzoate esters, and Fig. 6 is a con-venvoltage at which gas ionization leading to breaktiohalizod Vertical Section of a high q cy down occurs in mica capacitors is relatively low, Capacitor Containing liqu d ben oate ester.

and impregnation of' mica capacitors is diflicult The following are examples of high frequency due to the imperviousness of mica. benzoate dielectric materials which are suitable I have discovered that liquid organic esters use in accordance With my invention; ethyl of the benzoate type, and mixtures of such esters, benzoate. butyl b t s pr pyl enz at are well suited for dielectric function in high benzyl benzoate.butyltriohlorbenzoateand myi frequency capacitors, My present invention M trichlor benzoate. As will be later shown mixprises capacitors containing liquid benzoate W165 of 511011 esters remain q at extremely esters as dielectric elements. loW temperatures- The properties of liquid dielectric materials t an ambient temperature f ut 25 C.. all when subjected to high fre en ie t t, is, freof the above-enumerated benzoates are thin quencies well above about 10 kilocycles, are quite mobile liquids- Their s si y at 37.8 C. (1 00 unlike the properties of liquid dielectrics at ordi- A is Within the range of 3 t3o 0 Seconds aynary low frequencies. In commercial alternatbolt Universal While their p p s difier ing current circuits, the conventional frequencies Slightly, ey a e a ow, being ingeneral within are of the order of 25 to 60 cycles. Commonly, the range of about to yl benliquid dielectric materials which have been found 45 zoom constitutes an exception- It has a h in low frequency circuits to possess suitably high point of ut 7 to 1 which, however, can dielectric. constantand which have operatedwit be used under most commonly encountered temloW dielectric losses, have been found in high, perature conditions, the congealing point being frequency circuits to have impracticable electrical W below room mp ra ure. The pour point characteristics such as low dielectric constant, or can be loWeIod if desired by blending it h other high energy losses, or both, suitably selected benzoates.

In parti ula esters f benzoic d have been The dielectric constant of benzoate esters is characterized by such high dielectric lossat low higher than the commonly b erved dielectric frequencie (SQ-cycles) v at l impressed constant of other organic esters, the dielectric voltagestha-t they have-been considered as wholly constant at room temperatures of the various unsuited for embodiment in electric capacitors. esters above enumerated being at least as: high Some of the benzoates were found to operate, in as about capacitors, when tested on. cycle circuits. with. Fig. i shows a dielectric constant at 25 C; of

power factors as high as 50 per cent, half of the benzyl benzoate, graph. 1, and isopropylbenzoater input energy was lost and appeared as undesired Go graph 2, over the high frequency range of about 100 to 1000 kilocycles. It will be observed that the dielectric constant of benzyl benzoate at 140 kilocycles is above 5, and is very nearly constant over the entire range of frequencies. A slight increase may be noted over a frequency of about 700 to 1000 kilocycles. The dielectric constant of isopropyl benzoate, graph 2, is slightly below 5 when measured with frequency of 140 kilocycles and is constant over the range of 300 to 1000 kilocycles.

As shown in Fig. 2, the dielectric constant of four benzoate esters decreases somewhat with rise of temperature. Graphs 3, 4, 5 and 6, respectively, show the characteristic of butyl trichlor benzoate,

amyl trichlor benzoate, benzyl benzoate and 1250- propyl benzoate.

Fig. 3 shows the power factor characteristic of two benzoate esters over a range of high frequencies. Graph 1 shows the characteristic of isopropyl benzoate, and graph 8 the characteristic of benzyl benzoate.

Fig. 4 shows the power factor in per cent over a working temperature range. Graph 9, for amyl trichlor benzoate, shows the power factor to be slightly above at a temperature of about C., and then to drop rapidly as the temperature rises to the working range of temperatures of approximately 50 C., or higher. Graph l0 shows that butyl trichlor benzoate has a somewhat similar power factor-temperature characteristic. The power factor at about 25 C. is about .17 and decreases to about 07% when the temperature rises to about 75 C. Graph I! shows the power factor-temperature characteristic of isopropyl benzoate. benzyl benzoate, graph I2, is very low, approximating about .03% over the entire range of temperature of 25 to 100 C. In general the power factor of benzoate dielectric elements are well within a permissible working range over the range of operating temperatures. Benzyl benzoate, which has high dielectric constant and low power factor over a range of frequencies and over a range of temperatures, is a preferred high frequency dielectric material in capacitors.

In Fig. 5 are shown pour points (or crystallizing points) of several benzoate mixtures comprising benzyl benzoate as one component. Graph it shows the liquidity characteristic of mixtures of benzyl benzoate and tetrahydro furfuryl benzoate. Even small additions of latter result in a relatively great lowering of the congealing temperature. As shown by graph it benzoate dielectric compositions consisting of mixtures of about 80 to 90 per cent benzyl benzoate and about 20 to 10 per cent of tetrahydro furfuryl benzoate are in the liquid state at temperatures over a range of temperatures the low limit of which is about C, Graph I4 shows the efiect of amyl trichlor benzoate addition to benzyl bentzoate. Mixtures containing about to 70 per cent of the amyl trichlor benzoate congeal at a temperature of about 50 C. Graph similarly shows the congealing characteristics of a range of mixtures of benzyl benzoate and isopropyl benzoate. Mixtures containing about 50 to per cent of the latter remain liquid down to 60 C.

The liquid high frequency dielectricmaterials of the benzoate ester type may be employed in conventional capacitors heretofore used for the high frequency field. As indicated in Fig. 6 such capacitors may comprise spaced armatures i 6, i1 contained in a tank [8. The space between the The power factor of armatures, as indicated in Fig. 6, may be wholly filled with a liquid benzoate ester dielectric material l9. In some cases, suitable spacers, as indicated at 20, consisting of inert material, may partly fill the space between the armatures, the space, however, being largely unobstructed. While in some cases it is convenient to employ such spacers between the armatures, the are not essential and may be omitted. In any event the space between the armatures should be mainly unobstructed. The paper spacers commonly used in low frequency capacitors should not be used in the high frequency capacitors embodying my present invention. The illustration of the armatures I6, [1, which are shown connected to external terminals 2|, 22 is diagrammatic. Suitable construction for high frequency capacitors is shown in a copending application, Serial No. 500,806, filed September 1, 1943 (now abandoned) which is assigned to the same assignee as the present application.

In a capacitor containin benzyl benzoate as the sole dielectric material and constructed as conventionally indicated, a slow rise of operating temperature occurs from initial temperature of 25 C. to a steady operating temperature of about 45 C. or 50 C. in the course of about an hour of operation. During subsequent operation, the dielectric losses which appear as heat should be dissipated at such rate that the operating temperature remains substantially constant.

What I claim as new and desire to secure by Letters Patent of the United States, is:

l. A liquid dielectric material consisting of an ingredient selected from the class consisting of tetrahydro furfuryl benzoate, 10 to 25 per cent; amyl trichlor benzoate, 50 to per cent and isopropyl benzoate, 50 to 60 per cent, the remainder in each instance being benzyl benzoate, said dielectric material remaining liquid at a temperature below 45 C.

2. A liquid dielectric material consisting of a mixture of about 40 to 50 per cent of benzyl benzoate and about 60 to 50 per cent of isopropyl benzoate, said mixture remainin liquid over a range of temperature down to about 60 C.

3. A dielectric material consisting of a liquid mixture of about 75 to per cent benzyl benzoate and about 25 to 10 per cent of tetrahydro furfuryl benzoate, said mixture remaining liquid over a range of temperature down to about 45 C.

4. A dielectric material consisting of a liquid mixture of about 20 to 50 per cent of benzyl benzoate and about 80 to 50 per cent of amyl trichlor benzoate, said mixture remaining liquid over a range of temperature down to about 50 C.

FRANK M. CLARK.

REFERENCES CITED The following references file of this patent:

UNITED STATES PATENTS are of record in the OTHER REFERENCES Elektrische Dipolmomente Von Organischen Moiekulen, Zeitschrift Fur Physikali. 

